Vacuum-assisted securing apparatus for a microwave ablation instrument

ABSTRACT

A securing apparatus for selectively securing an ablating element of an ablation instrument proximate to a targeted region of a biological tissue. The securing apparatus includes a support base affixed to the ablation instrument relative the ablating element, and having a support face adapted to seat against the biological tissue proximate to the ablation element. The support base further defines a passage having one end communicably coupled to a vacuum source and an opposite end terminating at an orifice at the support face. The support face together with the biological tissue forms a hermetic seal thereagainst during operation of the vacuum source to secure the ablation instrument thereagainst. Essentially, the hermetic seal and the vacuum source cooperate to form a vacuum force sufficient to retain the ablation device against the biological tissue.

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present application is a Continuation-In-Part of U.S. patentapplication Ser. No. 09/178,066, filed Oct. 23, 1998, and entitled,“Directional Reflector Shield assembly For a Microwave AblationInstrument”, which is incorporated herein by reference in its entiretyfor all purposes.

BACKGROUND OF THE INVENTION

[0002] 1. Field of Invention

[0003] The present invention relates, generally, to ablation instrumentsystems that use electromagnetic energy in the microwave frequencies toablate internal bodily tissues, and, more particularly, to antennaarrangements and instrument construction techniques that direct themicrowave energy in selected directions that are relatively closelycontained along the antenna.

[0004] 2. Description of the Prior Art

[0005] It is well documented that atrial fibrillation, either alone oras a consequence of other cardiac disease, continues to persist as themost common cardiac arrhythmia. According to recent estimates, more thantwo million people in the U.S. suffer from this common arrhythmia,roughly 0.15% to 1.0% of the population. Moreover, the prevalence ofthis cardiac disease increases with age, affecting nearly 8% to 17% ofthose over 60 years of age.

[0006] Although atrial fibrillation may occur alone, this arrhythmiaoften associates with numerous cardiovascular conditions, includingcongestive heart failure, mitral regurgitation, hypertensivecardiovascular disease, myocardial infarcation, rheumatic heart disease,and stroke. Regardless, three separate detrimental sequelae result: (1)a change in the ventricular response, including the onset of anirregular ventricular rhythm and an increase in ventricular rate; (2)detrimental hemodynamic consequences resulting from loss ofatroventricular synchrony, decreased ventricular filling time, andpossible atrioventricular valve regurgitation; and (3) an increasedlikelihood of sustaining a thromboembolic event because of loss ofeffective contraction and atrial stasis of blood in the left atrium.

[0007] Atrial arrhythmia may be treated using several methods.Pharmacological treatment of atrial fibrillation, for example, isinitially the preferred approach, first to maintain normal sinus rhythm,or secondly to decrease the ventricular response rate. While thesemedications may reduce the risk of thrombus collecting in the atrialappendages if the atrial fibrillation can be converted to sinus rhythm,this form of treatment is not always effective. Patients with continuedatrial fibrillation and only ventricular rate control continue to sufferfrom irregular heartbeats and from the effects of impaired hemodynamicsdue to the lack of normal sequential atrioventricular contractions, aswell as continue to face a significant risk of thromboembolism.

[0008] Other forms of treatment include chemical cardioversion to normalsinus rhythm, electrical cardioversion, and RF catheter ablation ofselected areas determined by mapping. In the more recent past, othersurgical procedures have been developed for atrial fibrillation,including left atrial isolation, transvenous catheter or cryosurgicalablation of His bundle, and the Corridor procedure, which haveeffectively eliminated irregular ventricular rhythm. However, theseprocedures have for the most part failed to restore normal cardiachemodynamics, or alleviate the patient's vulnerability tothromboembolism because the atria are allowed to continue to fibrillate.Accordingly, a more effective surgical treatment was required to curemedically refractory atrial fibrillation of the heart.

[0009] On the basis of electrophysiologic mapping of the atria andidentification of macroreentrant circuits, a surgical approach wasdeveloped which effectively creates an electrical maze in the atrium(i.e., the MAZE procedure) and precludes the ability of the atria tofibrillate. Briefly, in the procedure commonly referred to as the MAZEIII procedure, strategic atrial incisions are performed to preventatrial reentry and allow sinus impulses to activate the entire atrialmyocardium, thereby preserving atrial transport functionpostoperatively. Since atrial fibrillation is characterized by thepresence of multiple macroreentrant circuits that are fleeting in natureand can occur anywhere in the atria, it is prudent to interrupt all ofthe potential pathways for atrial macroreentrant circuits. Thesecircuits, incidentally, have been identified by intraoperative mappingboth experimentally and clinically in patients.

[0010] Generally, this procedure includes the excision of both atrialappendages, and the electrical isolation of the pulmonary veins.Further, strategically placed atrial incisions not only interrupt theconduction routes of the common reentrant circuits, but they also directthe sinus impulse from the sinoatrial node to the atrioventricular nodealong a specified route. In essence, the entire atrial myocardium, withthe exception of the atrial appendages and the pulmonary veins, iselectrically activated by providing for multiple blind alleys off themain conduction route between the sinoatrial node to theatrioventricular node. Atrial transport function is thus preservedpostoperatively as generally set forth in the series of articles: Cox,Schuessler, Boineau, Canavan, Cain, Lindsay, Stone, Smith, Corr, Change,and D'Agostino, Jr., The Surgical Treatment Atrial Fibrillation (pts.1-4), 101 THORAC CARDIOVASC SURG., 402-426, 569-592 (1991).

[0011] While this MAZE III procedure has proven effective in ablatingmedically refractory atrial fibrillation and associated detrimentalsequelae, this operational procedure is traumatic to the patient sincesubstantial incisions are introduced into the interior chambers of theheart. Consequently, other techniques have thus been developed tointerrupt and redirect the conduction routes without requiringsubstantial atrial incisions. One such technique is strategic ablationof the atrial tissues through ablation catheters.

[0012] Most approved ablation catheter systems now utilize radiofrequency (RF) energy as the ablating energy source. Accordingly, avariety of RF based catheters and power supplies are currently availableto electrophysiologists. However, radio frequency energy has severallimitations including the rapid dissipation of energy in surface tissuesresulting in shallow “burns” and failure to access deeper arrhythmictissues. Another limitation of RF ablation catheters is the risk of clotformation on the energy emitting electrodes. Such clots have anassociated danger of causing potentially lethal strokes in the eventthat a clot is dislodged from the catheter.

[0013] As such, catheters which utilize electromagnetic energy in themicrowave frequency range as the ablation energy source are currentlybeing developed. Microwave frequency energy has long been recognized asan effective energy source for heating biological tissues and has seenuse in such hyperthermia applications as cancer treatment and preheatingof blood prior to infusions. Accordingly, in view of the drawbacks ofthe traditional catheter ablation techniques, there has recently been agreat deal of interest in using microwave energy as an ablation energysource. The advantage of microwave energy is that it is much easier tocontrol and safer than direct current applications and it is capable ofgenerating substantially larger lesions than RF catheters, which greatlysimplifies the actual ablation procedures. Typical of such microwaveablation systems are described in the U.S. Pat. Nos. 4,641,649 toWalinsky; 5,246,438 to Langberg; 5,405,346 to Grundy, et al.; and5,314,466 to Stern, et al, each of which is incorporated herein byreference.

[0014] Most of the existing microwave ablation catheters contemplate theuse of longitudinally extending helical antenna coils that direct theelectromagnetic energy in a radial direction that is generallyperpendicular to the longitudinal axis of the catheter although thefields created are not well constrained to the antenna itself. Althoughsuch catheter designs work well for a number of applications, suchradial output, while controlled, is inappropriate for use in MAZE IIIprocedures for example which require very strategically positioned andformed lesions. Thus, it would be desirable to provide microwaveablation catheter designs that are capable of effectively transmittingelectromagnetic energy that more closely approximates the length of theantenna, and in a specific direction, such as generally perpendicular tothe longitudinal axis of the catheter but constrained to a selectedradial region of the antenna.

SUMMARY OF THE INVENTION

[0015] The present invention provides a securing apparatus forselectively securing an ablating element of an ablation instrumentproximate to a targeted region of a biological tissue. The securingapparatus includes a support base affixed to the ablation instrumentrelative the ablating element, and having a support face adapted to seatagainst the biological tissue proximate to the ablation element. Thesupport base further defines a passage having one end communicablycoupled to a vacuum source and an opposite end terminating at an orificeat the support face. The support face together with the biologicaltissue forms a hermetic seal thereagainst during operation of the vacuumsource to secure the ablation instrument thereagainst. Essentially, thehermetic seal and the vacuum source cooperate to form a vacuum forcesufficient to retain the ablation device against the biological tissue.

[0016] In one embodiment, the support face is deformable tosubstantially conform to the shape of the biological tissue. One suchdeformable support face would be in the form of a suction cup. Inanother form, the orifice is provided by a proximal orifice positionedon a proximal end of the window portion, and a distal orifice positionedon a distal end of the window portion. The orifices may also be providedby a plurality of orifices spaced apart peripherally about the windowportion.

[0017] In another aspect of the present invention, a securing apparatusis provided for selectively securing an ablating element of an ablationinstrument proximate to a targeted region of a biological tissue. Thesecuring apparatus includes a support base coupled to the ablationinstrument, and which defines a passage terminating at an orificepositioned to receive the biological tissue during ablation of theablating element. A vacuum line is in fluid communication with thesupport member passage; and a vacuum source is operatively coupled tothe vacuum line. Upon the generation of a vacuum force by the vacuumsource, sufficient to hermetically seal the support member against thebiological tissue, the ablation instrument will be secured thereto.

[0018] In still another embodiment, a microwave ablation instrument forablating biological tissue is provided including a transmission linehaving a proximal portion suitable for connection to an electromagneticenergy source, and an antenna coupled to the transmission line forgenerating an electric field sufficiently strong to cause tissueablation. A shield assembly is coupled to the antenna to substantiallyshield a surrounding area of the antenna from the electric fieldradially generated therefrom while permitting a majority of the field tobe directed generally in a predetermined direction. The shield assemblyincludes a support base having a support face adapted to seat againstthe biological tissue proximate to the antenna. A passage is defined bythe support base having one end coupled to a vacuum source and anopposite end terminating at an orifice at the support face; wherein thesupport face forms a hermetic seal against the biological tissue duringoperation of the vacuum source to secure the ablation instrumentthereto.

[0019] Preferably, the transmission line is suitable for transmission ofmicrowave energy at frequencies in the range of approximately 800 to6000 megahertz. This electric field should be sufficiently strong tocause tissue ablation in a radial direction.

[0020] In another aspect of the present invention, a method is providedfor securing an ablation element of an ablation instrument to abiological tissue to be ablated. The method includes introducing theablation instrument into a patient's body to position the ablatingelement of the ablation instrument adjacent to the biological tissue tobe ablated; and contacting a support face of the ablation instrumentagainst the biological tissue to be ablated, the support face definingan orifice in communication with a vacuum source. The method furtherincludes creating a hermetic seal between the support face and thecontacted biological tissue through the vacuum source to secure theablating element in contact with the biological tissue; and ablating thebiological tissue with the ablation element.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The assembly of the present invention has other objects andfeatures of advantage which will be more readily apparent from thefollowing description of the best mode of carrying out the invention andthe appended claims, when taken in conjunction with the accompanyingdrawing, in which:

[0022]FIG. 1 is a diagrammatic top plan view, in cross-section, of amicrowave ablation instrument system with a directional reflectiveshield assembly constructed in accordance with one embodiment of thepresent invention.

[0023]FIG. 2 is an enlarged, fragmentary, top perspective view of theshield assembly of FIG. 1 mounted to an antenna assembly of the ablationinstrument system.

[0024]FIG. 3 is a side elevation view, in cross-section, of the shieldassembly of FIG. 2.

[0025]FIG. 4 is a front elevation view of the shield assembly takensubstantially along the plane of the line 4-4 in FIG. 3.

[0026]FIG. 5 is an exploded, side elevation view, in cross-section, ofthe shield assembly of FIG. 2, illustrating sliding receipt of an insertdevice in a cradle device of the shield assembly.

[0027]FIG. 6 is a fragmentary, side elevation view, in cross-section, ofa handle of the ablation instrument system of the present invention.

[0028]FIG. 7 is a diagrammatic side elevation view of a microwaveablation instrument system secured to a biological tissue with asecuring apparatus constructed in accordance with one embodiment of thepresent invention.

[0029]FIG. 8 is an enlarged, fragmentary, top perspective view of theantenna assembly of the ablation instrument system incorporating thesecuring apparatus of FIG. 7.

[0030]FIG. 9 is an enlarged, fragmentary, side elevation view, incross-section, of the securing apparatus of FIG. 8.

[0031]FIGS. 10A and 10B are, respectively, bottom plan and sideelevation views, partially broken away, of the securing apparatus ofFIG. 8 having a pair of deformable suction-type cups, in accordance withone embodiment of the present invention.

[0032]FIGS. 11A and 11B are respectively, fragmentary, bottom plan andside elevation views, in partial cross-section, of an alternativeembodiment securing apparatus having a fastener member for mounting tothe shield assembly.

[0033]FIG. 12 is an end view, in cross-section, of the base supporttaken substantially along the plane of the line 12-12 in FIG. 11B.

[0034]FIG. 13 is a bottom plan view, in partial cross-section, of analternative embodiment securing apparatus having a plurality oforifices, in accordance with one embodiment of the present invention.

[0035]FIG. 14 is a flow diagram of the relevant steps involved insecuring an ablation element of the ablation instrument to a biologicaltissue to be ablated in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0036] While the present invention will be described with reference to afew specific embodiments, the description is illustrative of theinvention and is not to be construed as limiting the invention. Variousmodifications to the present invention can be made to the preferredembodiments by those skilled in the art without departing from the truespirit and scope of the invention as defined by the appended claims. Itwill be noted here that for a better understanding, like components aredesignated by like reference numerals throughout the various FIGURES.

[0037] Turning now to FIGS. 1 and 2, a microwave ablation instrument,generally designated 20, is provided which includes a transmission line21 having a proximal portion 22 suitable for connection to anelectromagnetic energy source (not shown), and an antenna 23 coupled tothe transmission line 21 for radially generating an electric fieldsufficiently strong to cause tissue ablation. A shield assembly,generally designated 25, is coupled to the antenna 23 to substantiallyshield a peripheral area immediately surrounding the antenna from theelectric field radially generated therefrom while permitting a majorityof the :Field to be directed generally in a predetermined direction.

[0038] More specifically, a directional reflective shield assembly 25 isprovided for a microwave ablation instrument including a cradle device26 disposed about the antenna 23 in a manner substantially shielding asurrounding area of the antenna from the electric field radiallygenerated therefrom. The cradle device 26 further provides a windowportion 27 communicating with the antenna 23 which is strategicallylocated relative the antenna to direct a majority of the field generallyin a predetermined direction.

[0039] Accordingly, the shield assembly of the present invention enablespredetermined directional transmission of the electric field regardlessof the radial transmission pattern of the antenna. Tissue ablation canthus be more strategically controlled, directed and performed withoutconcern for undesirable ablation of other adjacent tissues which mayotherwise be within the electromagnetic ablation range radiallyemanating from the antenna. In other words, any other tissuessurrounding the peripheral sides of the antenna which are out of line ofthe window portion of the cradle will not be subjected to the directedelectric field and thus not be ablated. This ablation instrumentassembly is particularly suitable for ablation procedures requiringaccurate tissue ablations such as those required in the MAZE IIIprocedure above-mentioned.

[0040] It will be appreciated that the phrase “peripheral areaimmediately surrounding the antenna” is defined as the immediate radialtransmission pattern of the antenna which is within the electromagneticablation range thereof when the shield assembly is absent.

[0041] Transmission line 21, which is supported within a tubular shaft31, is typically coaxial, and coupled to a power supply (not shown)which is external to instrument 20. As best illustrated in FIGS. 2 and3, the microwave ablation instrument 20 generally includes an antenna 23with a proximal end 28 and a distal end 30. The proximal end 28 ofantenna 23 is grounded to an outer conductor (not shown) of transmissionline 21. The distal end 30 of antenna 23 is attached to center conductor32 of transmission line 21. Typically, antenna 23 is helical or in theform of a coil, i.e. an antenna coil, which is made from any suitablematerial, such as spring steel, beryllium copper, or silver-platedcopper. However, the antenna may be any other configuration, such as amonopole, or a lossy transmission line. The connection between theantenna 23 and center conductor 32 may be made in any suitable mannersuch as soldering, brazing, ultrasonic welding or adhesive bonding. Inother embodiments, the antenna 23 can be wound from the center conductorof the transmission line itself. This is more difficult from amanufacturing standpoint but has the advantage of forming a more ruggedconnection between the antenna and center conductor.

[0042] The outer diameter of antenna coil 23 will vary to some extentbased on the particular application of the instrument. By way ofexample, a instrument suitable for use in an atrial fibrillationapplication may have typical coil outer diameters in the range ofapproximately 0.07 to 0.10 inches. More preferably, the outer diameterof antenna coil 23 may be in the range of approximately 0.08 to 0.09inches.

[0043] The actual number of turns of the antenna coil may vary a greatdeal in accordance with the needs of a particular system. Some of thefactors that will dictate the number of turns used include the coildiameter and pitch, the desired length of the lesion, the antennaconfiguration, the instrument diameter, the frequency of theelectromagnetic energy, the desired field strength and the powertransfer efficiency within the tissue. Moreover, since these coiledantennas are preferably filled or cast with a silicone insulator toinsulate each coil from one another and from the center conductor, thepitch of the coils can be smaller and the number of turns increased. InMAZE III applications, for example, the antenna is comprised of aboutthirty-seven (37) turns, and has a length in the range of approximately19.8 mm to 20.0 mm. The antenna is typically spaced at least 0.5 mm, asfor example in the range of approximately 0.5 to 2.0 mm, from the distalend of the transmission line shield (not shown) and at leastapproximately 0.5 mm, as for example in the range of approximately 0.5to 1.0 mm from the distal end of the transmission line dielectric 33.

[0044] To substantially reduce or eliminate electromagnetic radiance ofthe distal end of the transmission line 21, the antenna is fed at itsresonance frequency to better define the electromagnetic field along thecoil. The antenna is preferably tuned by adjusting the length and thenumber of turns of the coil so that the resonance frequency of theradiative structure is in the range of about 2.45 GHz, for example.Consequently, the energy delivery efficiency of the antenna isincreased, while the reflected microwave power is decreased which inturn reduces the operating temperature of the transmission line.Moreover, the radiated electromagnetic field is substantiallyconstrained from the proximal end to the distal end of the antenna.Thus, when a longitudinally extending coil is used, the field extendssubstantially radially perpendicularly to the antenna and is fairly wellconstrained to the length of the antenna itself regardless of the powerused. This arrangement serves to provide better control during ablation.Instruments having specified ablation characteristics can be fabricatedby building instruments with different length antennas.

[0045] Briefly, the power supply (not shown) includes a microwavegenerator which may take any conventional form. When using microwaveenergy for tissue ablation, the optimal frequencies are generally in theneighborhood of the optimal frequency for heating water. By way ofexample, frequencies in the range of approximately 800 MHz to 6 GHz workwell. Currently, the frequencies that are approved by the U.S. Food andDrug Administration for experimental clinical work are 915 MHz and 2.45GHz. Therefore, a power supply having the capacity to generate microwaveenergy at frequencies in the neighborhood of 2.45 GHz may be chosen. Atthe time of this writing, solid state microwave generators in the 1-3GHz range are very expensive. Therefore, a conventional magnetron of thetype commonly used in microwave ovens is utilized as the generator. Itshould be appreciated, however, that any other suitable microwave powersource could be substituted in its place, and that the explainedconcepts may be applied at other frequencies like about 434 MHz, 915 MHzor 5.8 GHz (ISM band).

[0046] Referring back to FIGS. 2 and 3, the shield assembly of thepresent invention will be described in detail. In accordance with thepresent invention, cradle device 26 defines a window portion 27strategically sized and located to direct a majority of theelectromagnetic field generally in a predetermined direction. Cradledevice 26 is preferably tubular or cylindrical-shell shaped having aninterior wall 35 defining a cavity 36 extending therethrough which isformed for receipt of the antenna 23 therein. While the cradle device isshown and described as substantially cylindrical-shaped along thelongitudinal and cross-section dimensions, it will be appreciated that aplurality of forms may be provided to accommodate different antennashapes or to conform to other external factors necessary to complete asurgical procedure. For example, by longitudinally curving the antenna,either through manual bending or through manufacture, a curvilinearablative pattern may be achieved. Such a configuration, by way ofexample, may be necessary when ablating tissue around the pulmonaryveins in the MAZE III procedure

[0047] Cradle device 26 is preferably thin walled to minimize weightaddition to the shield assembly, while being sufficiently thick toachieve the appropriate microwave shielding as well as provide theproper mechanical rigidity to the antenna area. In the preferredembodiment, cradle device 26 is composed of a conductive, metallicmaterial which inherently functions as a reflector. The walls of thecradle device, therefore, are substantially impenetrable to the passageof microwaves emanating from the antenna. Moreover, a percentage ofmicrowaves may be reflected them back into the cavity 36, andsubsequently remitted out of window portion 27. One particularlysuitable material is stainless steel, for example, having a thickness inthe range of about 0.010 inches to about 0.025 inches, and morepreferably about 0.015 inches.

[0048] As mentioned, an elongated helical microwave antenna normallyemits an electromagnetic field substantially radially perpendicular tothe antenna length which is fairly well constrained to the length of thecoil regardless of the power used. Accordingly, the proximal and distalends of the cradle may not require shielding by the cradle device in thesame manner as that required radially perpendicular to the longitudinalaxis of the antenna.

[0049] As best viewed in FIGS. 4 and 5, window portion 27 preferablyradially extends through one side of the cradle and into the cavity 36,and further extends longitudinally along cradle in a directionsubstantially parallel to the longitudinal axis thereof. The length ofthe ablative radiation is therefore generally constrained to the lengthof the coil, and may be adjusted by either adjusting the length of theantenna (a helical antenna for example), or by adjusting thelongitudinal length of the window portion 27. To maximize efficiency,however, the length of the window portion 27 is generally a littlelonger than the longitudinal length of the antenna 23, by about 1-2 mmon each side. This allows reflections out of the window portion. It willbe appreciated, however, that the window portion may be collectivelydefined by a plurality of sections (not shown), or that the cradledevice may include more than one strategically positioned windowportion.

[0050] For a tubular cradle device 26, FIG. 4 illustrates that thecircumferential opening of the window portion 27 may extendcircumferentially from about 45° to about 180°, and most preferablyextend circumferentially about 160°. A substantial portion of thebackside of the antenna, therefore, is shielded from ablative exposureof the microwaves radially generated by the antenna in directionssubstantially perpendicular to the longitudinal axis 37 thereof. Thecircumferential dimension of window portion 27, hence, may varyaccording to the breadth of the desired ablative exposure withoutdeparting from the true spirit and nature of the present invention.

[0051] Accordingly, the predetermined direction of the ablativeelectromagnetic field radially generated from the antenna may besubstantially controlled by the circumferential opening dimension, thelength and the shape of the cradle window portion 27. Manipulating thepositioning of window portion 27 in the desired direction, thus,controls the direction of the tissue ablation without subjecting theremaining peripheral area immediately surrounding the antenna to theablative electromagnetic field.

[0052] Briefly, ablation instrument 20 includes a handle 38 coupled tothe antenna and the cradle device 26 through an elongated tubular shaft31. By manually manipulating the handle, the cradle window portion 27may be oriented and positioned to perform the desired ablation. Theshaft is preferably provided by a metallic hypotube which is mounted tothe metallic cradle device through brazing paste, welding or the like.Moreover, the shaft 31 is preferably bendable and malleable in nature toenable shape reconfiguration to position the antenna and the cradledevice at a desired orientation relative the handle. This enables thesurgeon to appropriately angle the window portion toward the targetedregion for tissue ablation. It will be appreciated, however, that thematerial of the shaft is further sufficiently rigid so that the shaft isnot easily deformed during operative use. Such materials, for example,includes stainless steel or aluminum having diameters ranging from about0.090 inches to about 0.200 inches with wall thickness ranging fromabout 0.050 inches to about 0.025 inches. Most preferably, the shaft is304 stainless steel having an outer diameter of about 0.120 inches and awall thickness of about 0.013 inches.

[0053] The resonance frequency of the antenna is preferably tunedassuming contact between the targeted tissue and the longitudinaldimension of the antenna 23 exposed by the window portion 27. Hence,should a portion of, or substantially all of, the exposed region of theantenna not be in contact with the targeted tissue during ablation, theresonance frequency will be adversely changed and the antenna will beuntuned. As a result, the portion of the antenna not in contact with thetargeted tissue will radiate the electromagnetic radiation into thesurrounding air. The efficiency of the energy delivery into the tissuewill consequently decrease which in turn causes the penetration depth ofthe lesion to decrease.

[0054] Thus, tissue contact with the antenna is best achieved placingand orienting the antenna longitudinally adjacent and into the cradlewindow portion 27, as viewed in FIGS. 3 and 4. The longitudinal axis 37of the antenna is thus off-set from, but parallel to, the longitudinalaxis 40 of cradle device 26 in a direction toward the window portion. Inthis regard, the antenna may generally be positioned closer to the areadesignated for tissue ablation. Moreover, by positioning the antennaactively in the window portion 27 of the cradle device, the transmissivepower of the antenna may be effected substantially along the fullcircumferential opening of the window portion 27.

[0055] This arrangement of positioning the antenna actively in thecradle window portion 27 is partially achieved by mounting a distalportion of shaft 31 in alignment with the window portion, and to aninterior wall 35 of cradle device 26. As shown in FIG. 3, the distal endof the shaft 31 extends through a proximal opening 41 into cavity 36 ofthe cradle device 26 which initially positions the longitudinal axis ofthe shaft and that of the cradle device substantially parallel oneanother. It will be appreciated, however, that these axes need not beparallel.

[0056] To maintain the electromagnetic field characteristics of theantenna during operative use, it is imperative to stabilize the positionof antenna 23 relative the cradle device 26. Relative position changesor antenna deformation may alter the resonant frequency of the antenna,which in turn, changes the field characteristics of the antenna.Accordingly, to stabilize the antenna 23 relative the cradle device 26,the shield assembly 25 further includes an insert device, generallydesignated 42, disposed in cradle device cavity 36 between the cradledevice and the antenna.

[0057] Insert device 42 includes a longitudinally extending recess 43formed and dimensioned for press-fit receipt of the antenna therein. Inaccordance with the present invention, the recess 43 is preferablycylindrical shaped and extends substantially longitudinally along asurface of the insert device. This configuration positions, stabilizesand retains the helical antenna 23 actively in the window portion 27 tomaximize exposure of the targeted tissue to the microwaves generated byantenna. The recess 43 further includes a directional port 45communicating with the recess 43 which aligns the same with the windowportion 27 of the cradle device 26 to direct the majority of the fieldgenerally in the predetermined direction. For a curvilinear antenna, itwill be understood that the recess may be similarly conformed.

[0058] The insert device 42 further performs the function of decreasingthe coupling between the antenna 23 and the metallic cradle device 26.Should the antenna be too close to the metallic surface of the cradledevice, a strong current may be induced at the surface thereof. Thissurface current will increase the resistive losses in the metal and thetemperature of the cradle device will increase. On the other hand,direct conductive contact or substantially close contact of the antennawith the metallic cradle device will cause the reflective cradle deviceto become part of the radiative structure, and begin emittingelectromagnetic energy in all directions.

[0059] Insert device 42 is therefore preferably provided by a gooddielectric material which is relatively unaffected by microwaveexposure, and thus capable of transmission of the electromagnetic fieldtherethrough. Preferably, this material is provided by a low-lossdielectric material such as TEFLON, silicone, or polyethylene,polyimide, etc.

[0060] Insert device 42 is preferably provided by a substantially solidcylindrical structure dimensioned for a sliding interference fit, in thedirection of arrow 46 (FIG. 5), through a distal opening 47 of thecradle device cavity 36. Thus, the outer diameter of the insert deviceis preferably slightly larger than the inner diameter of the cavity 36defined by cradle interior wall 35. A proximal portion of insert device42 includes a semicircular alignment tongue 48 formed to cooperate withthe distal end of the shaft 31 during sliding receipt of the insertdevice 42 in the cradle device 26 for alignment thereof. Moreover, adistal portion of the insert device 42 includes an annular shoulderportion 50 formed and dimensioned to contact a distal edge 51 of cradledevice 26 upon full insertion of insert device into cavity 36.Collectively, the alignment tongue 48 and the annular shoulder portion50 cooperate to properly align the recess 43 and the directional port45, and thus the press-fit antenna 23, in the window portion 27 of thecradle device. Moreover, for reasons to be discussed henceforth, thecircumferential dimension of the shoulder portion 50 is conformedsubstantially similar to that of the cradle device (FIG. 3).

[0061] By composing the cradle device 26 of a high conductivity metal, asuperior microwave reflector is produced. Thus, when an electromagneticwave originating from the antenna reaches the cradle device, a surfacecurrent is induced. That current will in turn generate a responsiveelectromagnetic field that will interfere with the incident field insuch a way that the total electromagnetic field in the cradle devicewill be negligible.

[0062] While a majority of the electromagnetic energy is reflected bythe metallic cradle device 26, since it is not a perfect conductor, afraction of the incident electromagnetic energy is absorbed by resistivelosses therein. Consequently, the cradle device 26 itself may eventuallygenerate heat in an amount detrimental to the surrounding tissue. Theshield assembly 25 of the present invention, therefore, preferablyincludes an insulator 52 disposed about the cradle device 26 to insulatethe surrounding tissues from the cradle device. As best viewed in FIGS.2-4, insulator 52 is disposed peripherally about the cradle device 26 ina manner conductively contacting the outer surface thereof andparticularly substantially along its length dimension.

[0063] The insulator 52 provides a longitudinally extending bore 53formed and dimensioned for sliding receipt of the cradle device 26therein. Preferably, such sliding receipt is performed through aninterference fit to insure conductive contact between the insulator andthe cradle device. Accordingly, the insulator 52 further performs thefunction, in part, of a heat sink for the transfer and dissipation ofheat into the insulator 52 from the cradle device 26.

[0064] Similar to the insert device 42, the insulator 52 defines adirectional window 55 extending into the bore 53 from a side wallthereof. This directional window 55 is aligned to communicate with thewindow portion 27 of the cradle device 26 and the directional port 45 ofthe insert device 42 so that the cradle device can direct the majorityof the field generally in the predetermined direction. Preferably, asviewed in FIG. 4, the directional window 55 of the insulator 52 iscircumferentially dimensioned slightly smaller than or substantiallyequal to the circumferential dimension of the window portion 27 ofcradle device 26. This arrangement minimized exposure of the edgesdefining the window portion 27 to tissues during operation.

[0065] To appropriately cool the cradle device during operational use,the insulator 52 must be designed with a sufficient heat transfercapacity to transfer and dissipate the heat continuously generated bythe cradle device. One factor determining both the insulatory and heatsink capacity is the material composition. The insulator material,however, preferably has a low loss-tangent and low water absorption sothat it is not itself heated by the microwaves. In accordance with thepresent invention, the insulator is preferably provided by a suitablethermoplastic material such as ABS plastic.

[0066] The other primary factor determining the heat sink capacity isthe volume of the insulator contacting the cradle device. FIGS. 3 and 4best illustrate that the insulator 52 is preferably substantiallycylindrical-shaped in conformance with the peripheral dimensions of thecradle device 26. The longitudinal axis of bore 53 is off-set from thatof the insulator 52 which functions to position the antenna 23 in thealigned windows, and collectively closer to tissues targeted forablation. Moreover, a backside of the insulator 52 is substantiallythicker and more voluminous than the opposed frontside thereof whichdefines the directional window 55. This configuration provides greaterheat sink capacity at the backside of the insulator 52 whichconductively contacts a substantial majority of the backside of cradledevice 26.

[0067] Bore 53 preferably includes a distal opening 58 therein which isformed for sliding receipt of the substantially uniform transversecross-sectional dimension of the cradle device 26. Sliding support ofthe insulator 52 longitudinally along the cradle device 26 continuesuntil a back wall 56 of the bore 53 contacts the proximal edge 57 of thecradle device 26. This functions to limit the insertion of the cradledevice 26 in the bore 53. At the distal end portion of the insulator 52,the annular shoulder portion 50 of the insert device 42 slideablycontacts the interior wall of the bore distal opening 58 to secure theinsulator to the cradle device and the insert device. Thecircumferential dimension of the shoulder portion 50 is preferablydimensioned to provide an interference fit with the shoulder portion.Thus, the outer diameter of the shoulder portion 50 is preferablyslightly larger than the inner diameter of the bore 53 of the insulator52. An adhesive, such as cyanoacrylate, may be applied to further securethe insulator in place.

[0068] As shown in FIGS. 2 and 3, once the insulator is properlypositioned, the distal end thereof is dimensioned to be positionedsubstantially flush with the distal end of the insert device 42.Further, the insert device 42 and the insulator 52 cooperate to enclosethe distal edge 51 of the cradle device therein.

[0069] Referring now to FIG. 6, a handle 38 for the ablation instrument20 will be described in detail. In the preferred form, the handle 38 iscomposed of a nonconductive, relatively rigid material, such as ABSplastic. As above-indicated, the handle 38 is provided as a vehicle tomanually manipulate the orientation and positioning of the cradle windowportion 27 during operational use. This is performed by rigidlyattaching the handle to a proximal end portion of the shaft 31.

[0070] At a distal portion of the handle 38, a passage 60 extendsaxially into an interior portion of the handle. The diameter of thepassage 60 is preferably substantially equal to the shaft diameter tominimize the tolerance therebetween. An interior wall 61 of the handleportion defines an axially extending cavity 36 which communicates withthe distal passage 60. The cavity 36 is preferably of a diameter largerthan that of the passage 60, and preferably extends through handle 38substantially coaxial with the passage 60.

[0071] The shaft is positioned in the handle passage 60 such that theshaft proximal end terminates in the cavity 36. To rigidly mount theshaft 31 to the handle 38, an insert screw (not shown) or the like, oran adhesive may be applied in the passage between the shaft 31 and thehandle 38.

[0072] As shown in FIG. 6, the transmission line 21 extends through theproximal cavity 36 and into the tubular shaft for coupling to theantenna 23. An elastic retraining device 62 may be provided mounted inthe cavity 36 at the proximal end of the handle which cooperates withthe transmission line 21 to mount the same to the handle.

[0073] Due to the conductive nature of the metallic hypotube or tubularshaft 31 and the coaxial arrangement between outer conductor of thecoaxial cable and the metallic shaft, a second transmission line isformed between these substantially concentric cylindrical metallicsurfaces. Electromagnetic energy emitted by the antenna excites thissecond transmission line which detrimentally propagates microwave energybetween metallic tube and the outer conductor of the coaxial cable.Thus, a part of the microwave energy is propagated back toward thehandle.

[0074] In accordance with the present invention, handle 38 furtherincludes a microwave absorbent 65 disposed peripherally around theproximal portion of the tubular shaft 31 to substantially absorbmicrowave radiation transmitted by the proximal end thereof. While themicrowave absorbent may be integrally formed in the materials composingthe handle, it is preferred that a material 65 containing the microwaveabsorbent be disposed or wrapped about the juncture 66 between proximalend 63 of the shaft 31 and transmission line 21, as shown in FIG. 6.

[0075] In the preferred embodiment, this material wrap 65 is a siliconbased microwave absorbent, such as C-RAM KRS-124 from Cuming MicrowaveCorp. having a thickness of about 0.085 inches. Moreover, this materialwrap 65 must be sufficient in length to extend over the juncture 66between the shaft proximal end 63 and the transmission line 21.Preferably, the wrap extends equidistant from the juncture 66 in eachdirection by about 0.25 inches to about 0.75 inches. This distance mayvary depending upon the anticipated amount of electromagnetic fieldtransmission, the material thickness and the type of microwave absorbentapplied.

[0076] In accordance with the present invention, to facilitate locationof the window portion 27 relative the handle 38 during operative use, amarking device 67 and method are provided. Such location marking isparticularly useful during operative use when the antenna and shieldassembly cannot be easily viewed.

[0077] Preferably, a visual or tactile marking device 67 (FIG. 6) islocated along the handle 38 to communicate to the surgeon the locationand orientation window portion. This visual marking may be provided by asimple depression mark, painted mark or illuminated mark, or the likeeasily viewed along the handle. This marking is preferably positionedand aligned in a plane bisecting the window portion 27 and the handle38. More preferably, as shown in FIG. 6, the marking is positioned onthe same side of the handle as the window portion 27. However, it willbe understood that the marking may be placed anywhere along the handle38 as long as the position thereof remains affixed relative the windowportion.

[0078] Although only a few embodiments of the present inventions havebeen described in detail, it should be understood that the presentinventions may be embodied in many other specific forms withoutdeparting from the spirit or scope of the inventions. Particularly, theinvention has been described in terms of a microwave ablation instrumentfor cardiac applications, however, it should be appreciated that thedescribed small diameter microwave ablation instrument could be used fora wide variety of non-cardiac ablation applications as well. The sizeand pitch of the described antenna coils may be widely varied. It shouldalso be appreciated that the longitudinally oriented antenna coil doesnot need to be strictly parallel relative to the shaft axis and indeed,in some embodiments it may be desirable to tilt the antenna coilsomewhat. This is especially true when the malleable shaft isreconfigured to the particular needs of the surgical application. Theantenna can also be flexible and malleable.

[0079] It should also be appreciated that the microwave antenna need notbe helical in design. The concepts of the present invention may beapplied to any kind of radiative structure, such as a monopole or dipoleantennas, a printed antenna, a slow wave structure antenna, a lossytransmission line or the like. Furthermore, it should be appreciatedthat the transmission line does not absolutely have to be a coaxialcable. For example, the transmission line may be provided by astripline, a microstrip line, a coplanar line, or the like.

[0080] The conventional technique employed to position and ablate thebiological tissue with the ablation instrument has been to manually holdthe handle of the ablation instrument in a manner causing the ablatingelement to contact against the targeted area. For the most part, whetheror not the ablating element is in contact with the targeted tissue, hasbeen determined by the surgeon's skill and experience with the aid ofimaging technology. The ablation device, however, is typically hard tomanipulate (e.g., user steadiness and moving tissues) and frequentlyrequires repositioning to ensure that the targeted area is beingproperly ablated. During a cardiac ablation procedure, for example, theheart may be moving away from the ablation element by as much as 1 cm.Consequently, it is fairly difficult to maintain continuous contactbetween the ablation element and the heart during these cardiacprocedures.

[0081] In view of above, it is desirable to provide an ablationinstrument that facilitates continuous contact with the targetedbiological tissue during the ablation procedure. As best viewed in FIGS.7-9 a securing apparatus, generally designated 68, is provided forselectively securing an ablation element 23 of an ablation instrument 20proximate to a targeted region of a biological tissue. The securingapparatus 68 includes a support base 69 having a support face 70 whichis adapted to seat against the biological tissue proximate to theablation element 23. The support face further defines a passage 72having one end communicably coupled to a vacuum source 75 and anopposite end terminating at an orifice 76 at the support face. Duringthe operation of the vacuum source 75, and while the orifice 76 issubstantially positioned against the biological tissue 77 (FIG. 7), thesupport face 70 is caused to form a hermetic seal with the biologicaltissue to secure the ablation instrument thereto. Thus, the securingapparatus facilitates the maintenance of continuous contact of theablation element against the targeted biological tissue to produce amore strategically positioned lesion.

[0082] Accordingly, upon proper manipulation and positioning of theablation element against targeted biological tissue, the orifices of thesecuring apparatus will be moved to an orientation seated adjacent thetargeted tissue. The securing apparatus 68 may then be activated togenerate a vacuum at the orifices 76′, 76″. In turn, the ablationelement can be continuously secured against the targeted tissue for theduration of the ablation.

[0083] Briefly, the ablation instrument 20 is, for example, preferablyprovided by the ablation instrument illustrated in FIGS. 1-3. Aspreviously described, the ablation instrument 20 includes a transmissionline 21, an antenna ablating element 23, a shield assembly 25, a shaft31, and a handle 38, which respectively communicate to direct a majorityof the field generally in a predetermined direction.

[0084] In accordance with one embodiment of the present invention, thesecuring apparatus 68 is configured to be integrally formed with theshield assembly 25 of the ablation instrument 20. In this configuration,the support base 69 of the securing apparatus 68 is integrally formedwith the cradle device 26 of the shield assembly 20. However, as will bediscussed in greater detail below, the support base may also beconfigured to be independent from the shield assembly (e.g., as aseparate member coupled to a portion of the shield assembly as shown inFIGS. 11A and 11B, or by replacing the shield assembly entirely).

[0085] Correspondingly, the support base 69 may be disposed about theantenna 23 such that the support floor 70 substantially surrounds theouter periphery of the antenna and forms window portion 27. Preferably,the support base is adjacent to the antenna to promote stability of thesecurement and to enable the antenna element to be as close to thebiological tissue as possible. As described, the window portion 27 isstrategically located relative to the antenna 23 and configured tocooperate with the antenna 23 to direct a majority of the fieldgenerally in a predetermined direction.

[0086] The support base 69, which in this embodiment is integral withthe cradle device 26, defines a passage 72 having one end communicablycoupled to a fluid line 74 and an opposite end terminating at an orifice76 at the support face 70. Thus, fluid line 74 is communicably coupledto passage 72. Preferably, the proximal end of the fluid line 74 isoperatively coupled to a vacuum source 75, which generates the vacuumnecessary to secure the ablating instrument to the biological tissue.The fluid line is preferably provided by a relatively thin diameterflexible Teflon tube of sufficient wall thickness to prevent collapseunder the vacuum, (e.g., medical grade). As shown in FIG. 8, the fluidline 74 is preferably disposed inside the tubular shaft 31 of theablation instrument 20 to minimize the collective diameter thereof. Inthe preferred form, therefore, the fluid line 74 extends through theshaft 31 and into the support base 69 for coupling to the passage 72. Itwill be appreciated, however, that the fluid line may be disposedexternal to the shaft 31 as well. It will also be appreciated that thevacuum lines can be independently connected to the vacuum source 75.

[0087] Briefly, the vacuum supply 75 includes a vacuum generator, whichmay take any conventional form, such as a vacuum pump or a venturivacuum generator (e.g. powered by a pressurized air or water supply).Furthermore, the vacuum generator may be part of the internal vacuumsupply system of a hospital or an external stand alone unit in theoperating room. In the preferred embodiment, the vacuum generatorproduces a vacuum in the range of about 30 mm Hg to about 60 mm Hg for apair of spaced-apart orifices 76′, 76″ having a diameter of about 1-2mm. It should be appreciated, however, that any other suitable vacuumsupply may be employed, and that other vacuum ranges may apply dependingupon the size of the orifice.

[0088]FIGS. 8 and 9 best illustrate that the proximal orifice 76′ ispositioned on a proximal end of the window portion 27 while the distalorifice 76″ is positioned on a distal end thereof. Preferably, theorifices are disposed proximate to the antenna, and on opposite ends ofthe window portion. This arrangement best maintains securement to thetargeted tissue, and thus the antenna alignment, when the securementapparatus 68 is activated during ablation. As will be described ingreater detail below and as shown in FIG. 13, the securing apparatus mayinclude a plurality of orifices 76 spaced-apart peripherally aroundwindow portion 27, or may be provided a single strategically positionedorifice (not shown).

[0089] As set forth above, the vacuum force necessary to anchor theablation device to the tissue is dependent upon the geometry andtransverse cross-sectional dimension of the orifices. Therefore, theseparameters are configured to have the smallest cross-sectionaldimension, relative to the vacuum force, yet provide sufficientsecurement of the support face against the biological tissue withoutdamage thereto. Additionally, the orifice is sized to maintain theintegrity of the hermetic seal between the support face and thebiological tissue. Preferably, the orifices have a diameter in the rangeof about 1-2 mm for a vacuum source of about 30-60 mm Hg (at theorifices 76′ and 76″).

[0090] The support face 70 is further adapted to seat against thebiological tissue proximate to the antenna 23 and in a manner forming ahermetic seal against the biological tissue during operation of thevacuum source. This is performed by providing a support face which isrelatively smooth and non-porous which facilitates sealing against thetissue. While the support face is shown as smoothly curved (i.e.,cylindrical) along the longitudinal and cross section dimensions, itwill be appreciated that a plurality of forms may be provided toaccommodate external factors necessary to complete a surgical procedure.For example, the shape of the support face may be configured to coincidewith the shape of the biological tissue to further promote sealing.

[0091] Preferably, the support face 70 is dimensioned to verticallyalign the ablation element 23 against the targeted tissue. This contactensures that the majority of the electromagnetic field generated isdirected into the targeted tissue without subjecting the immediateperipheral area surrounding the ablating element to the ablativeelectromagnetic field. In this manner, the ablation element willeffectively and efficiently ablate the targeted biological tissue.

[0092] In one embodiment of the invention, the support face 70 may becomposed of a soft deformable material which is relatively firm yet cansubstantially conform to the surface of the targeted biological tissue.Such confirmation maintains seal integrity between the securingapparatus and the biological tissue so that a vacuum loss is less likelyduring the ablation procedure. For example, as shown in FIG. 10, thesupport face may include a pair suction cups 80′, 80″, communicablycoupled to the orifices 76′ and 76″. For the most part, a standardconnection used to couple the suction cups 80′, 80″ to the orifices 76′,76″. Upon application of the vacuum source the suction cups engage andconform to the contacting tissue for seal formation therebetween.

[0093] In an alternative embodiment of the present invention, thesecuring apparatus 68 is adapted to be retrofit to the shield assembly25 of FIGS. 1-6. In this embodiment, referring now to FIGS. 11A and 11B,the support base 69 of the securing apparatus 68 is removably coupled toa distal portion of the ablation instrument 20 through a fasteningmember 81. More particularly, this configuration removably mounts thesecuring apparatus 68 to the shaft 31 of the ablation instrument 20. Asshown in FIG. 12, support base 69 defines an aperture 82 extendingtherethrough which is formed for receipt of shaft 31. Hence, thefastening member 81 may affix to shaft 31 through an interference fittherewith or through a bolt-type fastener (not shown). In the preferredform, the support base 69 is C-shaped (FIG. 11B) having opposed legportions 83′, 83″ which extend around the shield assembly 25 andterminate at support faces 70′, 70″. Similar to the previous embodiment,these support faces are adapted to seat against the biological tissueduring ablation to create a hermetic seal for the respective orifices76′, 76″.

[0094] Furthermore, each leg portion 83′, 83″ of the support base 69defines passages 72′, 72″ each having one end communicably coupled to afluid line 74 and an opposite end terminating at a respective orifice76′, 76″ at the support face 70′, 70″. As best illustrated in FIG. 12,passage 72′ of leg portion 83′ is adapted to extend around aperture 82to avoid interference with the instrument shaft 31. While the retrofitembodiment of the present invention is illustrated as having opposed legportions 83′, 83″, at the proximal and distal ends of the shieldassembly 25, it will be appreciated that the support base may bedisposed at only one of the distal end and the proximal end of theshield assembly or on the sides of the window portion 27 thereof.

[0095] In yet another alternative embodiment, the securing apparatus mayinclude a plurality of spaced-apart orifices 76 peripherally extendingaround the window portion 27 of the securing apparatus (FIG. 13). Thisconfiguration enables a more secure mount to the biological tissue byproviding additional orifices surrounding the ablation element 23.Preferably, a plurality of vacuum lines (not shown) are provided toensure seal integrity of securing apparatus 68 in the event of leakageof one of the seals. For example, each vacuum line may be communicablycoupled to 1-3 orifices. Thus, a vacuum leak at one of these orificeswill not affect the seal integrity of the other vacuum lines. Thismultiple vacuum line concept may be applied to the other configurationsas well. Alternatively, these orifices 76 may be communicably coupled toonly one vacuum line.

[0096] In accordance with another aspect of the present invention, amethod is provided for securing the ablation element 23 of ablationinstrument 20 to a biological tissue 77 to be ablated. Referring now tothe flow diagram of FIG. 14, conventional pre-ablation events may applysuch as introducing the ablation instrument 20 into a patient's body toposition the ablating element 23 of the ablation instrument 20 adjacentto the biological tissue to be ablated. These pre-ablation steps (step100) are conventional and are readily understood by those skilled in theart.

[0097] Correspondingly, the first step 102 includes contacting thesupport face 70 of the support base 69 against the biological tissue tobe ablated. Once the ablation instrument is in the proper position(e.g., proximate the targeted tissue), the securing apparatus 68 may beactivated to secure the ablation instrument. Thus, at the second step104, the method may include creating a hermetic seal between the supportface 70 and the contacted biological tissue 77 with the vacuum source75. By creating a hermetic seal, the ablating element (e.g., antenna) issecured to the biological tissue 77 in the desired direction.

[0098] After the ablation instrument 20 is secured to the tissue 77, thethird step 106, of ablating the biological tissue with the ablationelement 23 may commence. By securing the ablation instrument to thebiological tissue, the ablation instrument is able to direct themajority of the field generally in the predetermined direction withoutsubjecting the immediate peripheral area surrounding the ablatingelement to the ablative electromagnetic field.

[0099] After ablation the targeted biological tissue, the fourth step108 may commence which involves reducing the vacuum and breaking thehermetic seal. This may be performed by simply pulling the ablationinstrument away from the targeted tissue, or by reducing the vacuumthrough a pressure valve or the like.

[0100] It should be appreciated that additional ablating steps may beneeded to complete the ablation procedure and therefore the foregoingsteps may be used several times before ending the ablation procedure.Thereafter, conventional post-ablation steps (step 110) are performedthat are well known to those skilled in the art and therefore, for thesake of brevity will not be discussed herein.

[0101] While this invention has been described in terms of severalpreferred embodiments, there are alterations, permutations, andequivalents which fall within the scope of this invention. It shouldalso be noted that there are many alternative ways of implementing themethods and apparatuses of the present invention.

[0102] By way of example, the secured ablation instrument may bedisengaged from the biological tissue with an air pulse. The fluid linemay further be coupled to the transmission line to form one combinationline, extending from the ablation instrument. Further still, the vacuumforce may be adjustably controlled with a flow controller or the like.Additionally, vacuum sensors may be employed to continuously monitor thevacuum applied to secure the ablation instrument to the biologicaltissue.

[0103] It is therefore intended that the following appended claims beinterpreted as including all such alterations, permutations, andequivalents as fall within the true spirit and scope of the presentinvention.

1. A securing apparatus for selectively securing an ablating element ofan ablation instrument proximate to a targeted region of a biologicaltissue comprising: a support base affixed to said ablation instrumentrelative said ablating element, and having a support face adapted toseat against the biological tissue proximate to the ablation element,and defining a passage having one end communicably coupled to a vacuumsource and an opposite end terminating at an orifice at the supportface; wherein said support face forms a hermetic seal against thebiological tissue during operation of said vacuum source to secure theablation instrument thereagainst.
 2. A securing apparatus as defined inclaim 1, further including a fastening member configured to couple thesupport base to the ablation instrument,
 3. A securing apparatus asdefined in claim 1, wherein the support face is dimensioned tovertically align the ablation element against the targeted tissue.
 4. Asecuring apparatus as defined in claim 1, wherein the hermetic seal andsaid vacuum source cooperate to form a vacuum force sufficient to retainsaid ablation device against said biological tissue.
 5. A securingapparatus as defined in claim 1, wherein the support face is deformableto substantially conform to the shape of the biological tissue.
 6. Asecuring apparatus as defined in claim 1, wherein the support face formssuction cup.
 7. A securing apparatus as defined in claim 1, wherein thesupport base is disposed proximate a distal end of the ablating element.8. A securing apparatus as defined in claim 1, wherein the support baseis disposed proximate a proximal end of the ablating element.
 9. Asecuring apparatus as defined in claim 1, wherein the support base andthe fastening member are integrally formed with the ablation instrument.10. A securing apparatus as defined in claim 1, wherein said supportface defines a window portion cooperating with the ablating element todirect a majority of an ablating field of the ablating element generallyin a predetermined direction
 11. A securing apparatus as defined inclaim 10, wherein said orifice includes a proximal orifice positioned ona proximal end of said window portion, and a distal orifice positionedon a distal end of said window portion.
 12. A securing apparatus asdefined in claim 11, wherein said orifice includes a plurality oforifices spaced apart peripherally about said window portion
 13. Asecuring apparatus as defined in claim 11, wherein said proximal anddistal orifices are about 1 mm to about 2 mm in diameter.
 14. A securingapparatus for selectively securing an ablating element of an ablationinstrument proximate to a targeted region of a biological tissuecomprising: a support base coupled to the ablation instrument, anddefining a passage terminating at an orifice positioned to receive thebiological tissue during ablation of the ablating element; a vacuum linein fluid communication with the support member passage; and a vacuumsource operatively coupled to the vacuum line, and formed to generate avacuum force sufficient to hermetically seal the support member againstthe biological tissue to secure the ablation instrument thereto.
 15. Asecuring apparatus as defined in claim 14, wherein the support face isdimensioned to vertically align the ablation element against thetargeted tissue.
 16. A securing apparatus as defined in claim 14,wherein the support face is deformable to substantially conform to theshape of the biological tissue.
 17. A securing apparatus as defined inclaim 14, wherein said support face defines a window portion cooperatingwith the ablating element to direct a majority of an ablating field ofthe ablating element generally in a predetermined direction
 18. Asecuring apparatus as defined in claim 17, wherein said orifice includesa proximal orifice positioned on a proximal end of said window portion,and a distal orifice positioned on a distal end of said window portion.19. A securing apparatus as defined in claim 18, wherein said orificeincludes a plurality of orifices spaced apart peripherally about saidwindow portion.
 20. A securing apparatus as defined in claim 17, whereinsaid proximal and distal orifices are about 1 mm to about 2 mm indiameter.
 21. A microwave ablation instrument for ablating biologicaltissue, comprising: a transmission line having a proximal portionsuitable for connection to an electromagnetic energy source; an antennacoupled to the transmission line for generating an electric fieldsufficiently strong to cause tissue ablation; and a shield assemblycoupled to the antenna to substantially shield a surrounding area of theantenna from the electric field radially generated therefrom whilepermitting a majority of the field to be directed generally in apredetermined direction, said shield assembly including: a support basehaving a support face adapted to seat against the biological tissueproximate to the antenna, and defining a passage having one end coupledto a vacuum source and an opposite end terminating at an orifice at thesupport face; wherein said support face forms a hermetic seal againstthe biological tissue during operation of said vacuum source to securethe ablation instrument thereto.
 22. A microwave ablation instrument asdefined in claim 21, wherein the transmission line is suitable fortransmission of microwave energy at frequencies in the range ofapproximately 800 to 6000 megahertz.
 23. A microwave ablation instrumentas defined in claim 21, wherein the antenna generates an electric fieldsufficiently strong to cause tissue ablation in a radial direction. 24.A securing apparatus as defined in claim 21, wherein the support face isdimensioned to vertically align the ablation element against thetargeted tissue.
 25. A securing apparatus as defined in claim 21,wherein the support face is deformable to substantially conform to theshape of the biological tissue.
 26. A securing apparatus as defined inclaim 21, wherein said support face defines a window portion cooperatingwith the ablating element to direct a majority of an ablating field ofthe ablating element generally in a predetermined direction
 27. Asecuring apparatus as defined in claim 26, wherein said orifice includesa proximal orifice positioned on a proximal end of said window portion,and a distal orifice positioned on a distal end of said window portion.28. A securing apparatus as defined in claim 27, wherein said orificeincludes a plurality of orifices spaced apart peripherally about saidwindow portion
 29. A securing apparatus as defined in claim 26, whereinsaid proximal and distal orifices are about 1 mm to about 2 mm indiameter.
 30. A method of securing an ablation element of an ablationinstrument to a biological tissue to be ablated, the method comprising:introducing the ablation instrument into a patient's body to positionthe ablating element of the ablation instrument adjacent to thebiological tissue to be ablated; contacting a support face of theablation instrument against the biological tissue to be ablated, saidsupport face defining an orifice in communication with a vacuum source;creating a hermetic seal between the support face and the contactedbiological tissue through the vacuum source to secure the ablatingelement in contact with the biological tissue; ablating the biologicaltissue with the ablation element; and
 31. The method as defined in claim30 further including: removing the vacuum and; breaking the hermeticseal for removal support face from the biological tissue.